This application requests funds to support a mentored Research Career Development Award ("K" series, CDA) for a candidate at Vanderbilt University. The candidate has formal training in chemistry and imaging sciences, and seeks to become an independent investigator within the field of molecular imaging. Funds to support this application will facilitate critical training in cancer biology, high-throughput screening, and mass spectrometry. A career development plan has been established that includes didactic training, laboratory training, and a research plan that ensures future success as an independent investigator. The proposed research seeks to develop quantitative, high-throughput screening (HTS) technology to accelerate the discovery and development of small molecule molecular imaging agents (MIAs). Ml is an emerging research tool and clinical discipline that aims to non-invasively characterize in vivo molecular processes at the cellular and sub-cellular levels. Currently, the MIA development paradigm is costly, time consuming, and narrow in scope. Given that genomic and proteomic technologies are now being used to rapidly discover novel molecular targets, there is a pressing need to develop new approaches which will accelerate the MIA discovery process. Here, we propose a library-based, HT approach that will enable the discovery of lead compounds with specificity for unique cellular phenotypes. Our approach will be universally applicable to numerous cell-based systems and facilitate quantification of compound uptake without the use of markers or labels. We will validate our methodology by screening for compounds able to selectively label various cell types found within the chronic inflammatory microenvironment of tumors. Under these proposed investigations, cellular-specific small molecules will be discovered in vitro and validated in vivo, with optimal candidates selected for future development as imaging agents. We will meet these goals by synergizing a small molecule HT screen with MALDI-QqTOF-MS according to the following specific aims: AIM 1- Develop a quantitative, HT method for screening cellular uptake of library-based small molecules. AIM 2- Identify small molecules from the HTS that will discriminate type-1, pro-inflammatory macrophages from type-2, anti-inflammatory macrophages and tumor cells. AIM 3- Validate the cellular specificity of lead compounds in vivo. Relevance to public health: In vivo molecular imaging agents are capable of measuring discrete, biological events associated with diseases such as cancer. The goal of this proposed CDA and research is to realize improved molecular imaging agents for translational research.